"The Heidi and Seal I knew was the couple everyone loves," says a fashion industry source who's worked with Klum, "super passionate and in love."

Sources who've witnessed Seal and Klum's typically overt shows of affection – "They were always all over each other, practically groping," says another fashion source, "totally in love" – are now left wondering what could have gone wrong for the pair, whose children are Leni, 7½, Henry, 6, Johan, 5, and Lou, 2.

"It has to be something major," says a Klum friend. "They have four kids together, and they've always been very committed to making it work."